1. Field of the Invention
This invention relates to a large size pneumatic rubber tire suitable for use in bad or rough roads. More particularly it relates to an improved tire adapted to be used in severe operating conditions as in earth-moving and construction vehicles and the like.
2. Description of the Prior Art
For such applications, in general, bias-structured tires have been mainly used, which include a bias carcass of multiple layer plies as a main reinforcement and a lug or block pattern tread in a rubber crown. In designing such a tire, the tread is made thicker from its center to tread edges in order to fulfill required cut-resistance, wear-resistance, heat-resistance and the like which are contradictory to one another. Troubles, particularly separation, due to heating derived from traveling of tires would occur in the proximity of shoulders which are thickest. In order to prevent such troubles, there have been proposed various solutions which, however, do not provide satisfactory results.
Depending upon requirements of utilization the tires have been obliged to operate in considerably severe conditions. For example, they are often used with high inner pressure for supporting heavy loads and at high speeds to obtain high operating efficiency. It has been found that the temperature in the tire under such a severe condition rises higher particularly between its center circumferential line and a location one fourth of a tread width therefrom than in shoulders. Hitherto known tread patterns cannot overcome the above heating of tires, and cannot fulfill the requirements of the wear-resistance, irregular wear-resistance and groove bottom crack-resistance.